Add v2 open API spec for ml sync (#136234) (#136873)

(cherry picked from commit b177ad9)

Co-authored-by: Lisa Cawley <lcawley@elastic.co>

x-pack/plugins/ml/common/openapi/README.md

@@ -4,17 +4,21 @@ The current self-contained spec file can be used for online tools like those fou
 
 A guide about the openApi specification can be found at [https://swagger.io/docs/specification/about/](https://swagger.io/docs/specification/about/).
 
+The `ml_apis_v3.yaml` file uses OpenAPI Specification Version 3.0.
+
+The `ml_apis_v2.json` file uses OpenAPI Specification Version 2.0.
+
  ## Tools
 
 It is possible to validate the docs before bundling them by running the following command in the `x-pack/plugins/ml/common/openapi/` folder:
   ```
-    npx swagger-cli validate ml_apis.yaml
+    npx swagger-cli validate ml_apis_v3.yaml
   ```
 
-Then generate the `bundled` files with the following commands:
+You can optionally generate `bundled` files with the following commands:
 
     ```
-    npx @redocly/openapi-cli bundle --ext yaml --output bundled.yaml ml_apis.yaml
-    npx @redocly/openapi-cli bundle --ext json --output bundled.json ml_apis.yaml
+    npx @redocly/openapi-cli bundle --ext yaml --output bundled.yaml ml_apis_v3.yaml
+    npx @redocly/openapi-cli bundle --ext json --output bundled.json ml_apis_v3.yaml
     ```